Joint replacement surgery seeks to replace portions of a joint with prosthetic components so as to provide long-lasting function and pain-free mobility.
During joint replacement surgery, one or more of the operative elements of the joint are replaced by prosthetic components. More particularly, many joints (e.g., the hip, the shoulder, etc.) comprise a ball-and-socket construction. During total joint replacement surgery, the head of the bone which provides the ball is replaced by a prosthetic ball-and-stem, and the portion of the bone which provides the socket is replaced by a prosthetic cup, whereby to provide the prosthetic total joint. In a partial joint replacement surgery, only one of the operative elements of the joint may be replaced, e.g., the head of the bone which provides the ball.
The present invention is directed to situations where the head of the bone which provides the ball is replaced by a prosthetic ball-and-stem, or where the head of the bone which provides the socket is replaced by a prosthetic socket-and-stem, as will hereinafter be discussed in further detail. For convenience, the present invention will generally be discussed in the context of replacing the head of a bone with a prosthetic ball-and-stem, although it should be appreciated that the present invention is equally applicable to situations where the head of a bone is replaced by a prosthetic socket-and-stem.
In order to replace the head of a bone with a prosthetic ball-and-stem, the head of the bone is first distracted from its socket so as to expose the head of the bone. Then an osteotomy is performed so as to remove the neck and head of the bone from the remainder of the bone. This action also exposes the intramedullary canal (sometimes hereinafter referred to as “the bone canal”) of the bone. Next, the proximal end of the bone canal is prepared to receive the stem of the prosthesis. More particularly, a rasp, reamer, broach, etc. is used to hollow out, clean and enlarge the proximal end of the bone canal so as to create an elongated cavity which will receive the stem of the prosthesis. Finally, the stem of the prosthesis is inserted into the bone canal so that the ball of the prosthesis is appropriately presented to the socket.
Typically, the ball of the prosthesis is manufactured separately from the stem of the prosthesis, with the ball component and the stem component being united at the time of use, although it is also possible to form the ball integral with the stem at the time of manufacture.
Furthermore, it should also be appreciated that, during the surgery itself, it is common to temporarily position a selected trial stem in the bone, attach a selected trial ball to the positioned trial stem, and then temporarily reduce the joint so as to confirm the joint reconstruction before the actual prosthetic stem is secured in position within the bone.
It will be appreciated that, when replacing the head of a bone with a prosthetic ball-and-stem, the surgeon must consider the position of the prosthetic ball relative to the socket, and that this must be done in both longitudinal and rotational terms. Specifically, the surgeon must consider (i) the longitudinal position of the prosthetic ball relative to the socket, and (ii) the rotational position of the prosthetic ball relative to the socket. This is necessary because, if either the longitudinal position or the rotational position of the prosthetic ball is “off” (i.e., mispositioned) vis-à-vis the socket, the ball will not seat properly in the socket and the prosthesis will not function as intended. As a practical matter, these positioning considerations require that a large inventory of prosthetic devices, of differing lengths and with differing angular orientations, must be maintained so that the prosthetic ball can be properly positioned in the patient. However, this is a costly requirement, and failures in inventory re-stocking can result in cancelled surgeries.